Pregnancy Due Date Calculator
Estimates a due date from the last menstrual period (Naegele’s rule).
Every calculation runs instantly in your browser, so your inputs are never sent to a server, and the tool is free with no sign-up. You can save the results as an Excel file with live formulas and reuse them later.
Inputs
- First day of last period
Example calculation
Estimated due date: 2026-10-08
| Estimated conception | 2026-01-15 |
|---|---|
| Due day of week | Thursday |
Method & notes
Naegele’s rule: last period + 280 days (40 weeks). An estimate; confirm with a doctor.
Tips
Change any input and the result recalculates in real time. After downloading the Excel file, you can reuse it by editing only the yellow input cells.
FAQ
How does the Pregnancy Due Date Calculator work?
Estimates a due date from the last menstrual period (Naegele’s rule). Naegele’s rule: last period + 280 days (40 weeks). An estimate; confirm with a doctor.
Can I save the results?
Yes. You can download the results for free as an Excel (.xlsx) file with live formulas that recalculate when you change the yellow input cells.
Is it free?
Yes — all Calcova calculators are free, and you can save results as an Excel file.